Multi -Secondary Transformer Analysis using Finite Element Method

Abstract

Power Transformers with more than one secondary winding are not uncommon in industrial applications. But new classes of applications where very large number of independent secondaries are use are becoming popular in controlled converters for medium and high voltage applications. Cascaded H-bridge medium voltage drives [1] and Pulse Step Modulation based high voltage power supplies are such applications [2]- [3]. In typical applications supplies having 35- 100 kV, 5-10 MW output with very fast dynamics (S order), such power supplies are widely used in fusion research [4]-[6]. Series connection of isolated voltage sources with conventional switching semi-conductor devices can be achieved by large number of separate transformers or by single unit of multi-secondary transformer. Naturally, a transformer having numbers of secondary windings (say 40) on single core is the preferred solution due to space and cost considerations.For design and simulation analysis of such a power supply, the model of a multi-secondary transformer poses special problem to any circuit analysis software as many simulation softwares transformer models with limited number (3-6) of secondary windings. Multi-Secondary transformer models with 3 different schemes are available[6].However behavior of the winding impedances and their spatial variance need to be modelled close to the actual transformer.A multi-secondary transformer shall be modelled in software which use FEM. This project covers the 3D Modeling and Analysis of transformer in COMSOL Multi Physics software. At each stage, validation of analysis result shall be done by actual transformer as wide variety of multi-secondary transformers are available at ITER-India, IPR.